Rods for flame spraying



ly 1967 I 'w. M. WHEILDON, JR 3,

RODS FOR FLAME SPRAYING Filed July 12, 1962 INVENTOR. WILL/AM MAXWELL WHE/LDON JE- AJ'TOENEY United States atent 3,329,558 RODS FOR FLAME SPRAYING William Maxwell Wheildon, Jr., Framingham, Mass., assignor to Norton Company, Worcester, Mass., :1 corporation of Massachusetts Filed July 12, 1962, Ser. No. 209,452 7 Claims. (Cl. 161-177) This invention relates to a slotted rod structure for coating articles by flame spraying and, more particularly, the invention comprehends a slotted rod having relatively deep, narrow slots formed at spaced points around its periphery.

Rods of this general character are well known, and a fluted type of rod is the subject of the Patent 3,171,774 of Wheildon and Hurd, for Rods for Flame Spraying, issued March 2, 1965.

This invention is an improvement on the fluted rod structure shown in the just mentioned pending application, the disclosure of which is hereby incorporated in its entirety in this application.

The rod of the pending application has a peripheral construction which it has been demonstrated speeds up spraying by increasing the surface area exposed to the flame used for fusing the rod. However, it has been found that when the flutes are too wide, and although the surface area of the rod is expanded so that more rapid fusing can take place, there occurs, on some occasions, an objectionable back flow of the acetylene flame from the melting tip, as well as some roll back of the molten material into the rod feed passage, either of which conditions of functioning are found to be objectionable by the operator of the gun. The present invention aims to cure these objections by producing a rod having relatively narrow, spaced, radially inwardly extending slots, as distinguished from the previously used flutes. The present invention, however, retains the general characteristics and advantages of the prior fluted rod, but, as stated, constitutes an improvement of substantial practical importance, both as regards the spraying efficiency on the one hand, and the elimination of possibility of jamming the rod such as is caused when an undue quantity of fused material rolls back and freezes in the rod passage, and possible apprehension on the part of an operator due to the reverse flow of hot gases which may escape lengthwise along the rod.

It is an object of this invention to provide an improved slotted flame spray rod having a structure which is essentially cylindrical for easy feed, and which will provide increased surface area to improve the rate of rod spraying or laydown.

Another object of this invention is to provide a rod structure which is capable of controlling thermal shock stresses better than any known rod structure.

Another object of the invention is to provide a rod that may be fused and sprayed in a manner to produce a more uniform coating.

All of these and other objects will become more apparent by reference to the drawing and the following detailed description.

In the drawings:

FIGURE 1 is an enlarged sectional side elevation partly broken away and showing the rod fusing and spraying end of a flame spraying gun in which the end of one rod of this invention is illustrated in relation to the leading end of another incoming rod, the leading edge of which latter is about to enter the fused zone;

FIGURE 2 is a detailed perspective view of the tip of the rod shown in FIGURE 1;

FIGURE 3 is a perspective view of a rod embodying the spaced, radially inwardly extending slots of this invention; and

FIGURES 4, 5, 6 and 7 are end views of the different size rods showing various spaced, radially inwardly extending slot arrangements.

The rod of this invention is especially adapted for use in the process heretofore shown and claimed in my Patent No. 2,707,691. In this patented disclosure, rods formed of a refractory oxide, a number of which are described, are fed into a nozzle 9, as shown in FIGURE 1. This spraying system has more recently been extended to spray other refractory materials in rod form such as borides, carbides, nitrides and refractory cermets, all of which refractory materials melt at a temperature above about 1000 C. An oxyacetylene flame or other hot gaseous zone is continuously maintained at the tip end of the nozzle and a refractory rod is fed through a passage in the nozzle 9 to be delivered into the hot gas zone. The tip end of the rod is melted by the heat and as the refractory material fuses, the molten phase is stripped from the rod to be conveyed onto a surface to be coated, as an atomized spray composed of the fused particles blown off of the end of the rod as it is progressively fed and melted. This is conventional procedure, and will not be further described since it will be readily understood by reference to my aforesaid patent.

The rod which is illustrated at 12 in FIGURE 3 may be of any practical diameter and I have sprayed rods of diameter up to rods of diameter but for most present day commercial spraying activities I prefer to use a rod that has a diameter of about A" and, as shown in FIG. 4, the rod has narrow, spaced, radially inwardly extending slots 11 which may be cut into its periphery when the rod is in green form by means of a thin blade. The slots as here shown extend longitudinally of the rod in a straight line generally parallel with the axis of the rod, as shown at 12, but it is not necessary that the slots follow such a direction and in certain instances, it may be advantageous to have spirally disposed or other curved paths for the slots which are disposed lengthwise of the rod. The rod may be formed in any conventional manner such as by extrusion in solid form and then the slots may be cut into its periphery, but I prefer to form it by extruding a suitable refractory material in the form of a particulate batch through a die which shapes the rod while simultaneously producing the slots in the periphery thereof. The slots are preferably produced in the rod prior to sintering and in a A" diameter rod they are preferably cut in from the periphery a distance to leave a solid portion 13 at least 4;" in diameter which extends through the rod from end to end, constituting a center core. The slots here shown are continuous from end to end but for some purposes the slots may be interrupted at spaced points to further control the back flow of hot gases which tend to push backwardly through the rod passage.

This rod can' be used as is after being sintered or if desired, can be formed to a more exact cylindrical form by being ground by running it through a centerless grinder. It has been found that using the preferred slot construction shown in FIGS. 47, the objectionable back flow of gases and molten material frequently met with in spraying with the conventional gun making use of the aforementioned fluted type of rod, is substantially eliminated. At the same time, the established desirable properties of the expanded surface area are improved upon by cutting the peripherally spaced, radially inwardly extending slots, as here shown, and the rod melts much more rapidly to provide a rate of spray that is appreciably faster than in the case of a conventional solid rod, as shown, for instance, in the patents to Ault, 2,876,121 and 2,882,174. Moreover, in use, the slotted rod of my invention has demonstrated desirable properties as regards resistance to thermal shock, and even when a crosswise crack appears in any quadrant, the rod continues to spray efficiently without spitting whereas in the past, a solid rod is rejected when a crack appears in its surface due to sintering because it has been found that thermal shock frequently causes such a rod to spit and produce an uneven spray pattern. It has been found that the narrow slots here shown promote the welding of the tip end of one rod to the other as the leading rod is used up, whereby to further control spitting.

The width of the slot in a rod of any outside diameter is preferably in the order of from .010 to .030 inch with the center portion 13 between the bottoms of the slots being preferably about As in diameter. The diameter of the center core as a practical matter is made at least because the center serves to support and sustain the rod and it must have adequate strength for handling and for spraying. Proportionately larger sizes of rods, of course, may be readily produced, and which may be sprayed more rapidly than the conventional solid rods or even the generally fluted structure shown in the aforesaid patent application.

In the drawings I have illustrated the presence of three longitudinally extending, radially inwardly projecting slots in FIG. 4, four such slots in FIG. 5, six in FIG. 6 and eight in FIG. 7, but any number of slots may be found useful in producing eflicient, rapid spraying while avoiding the described reverse flow, on the one hand, and in creasing the area which may be exposed to the flame for fusing the rod and spraying it, on the other. Furthermore, as pointed out, the rod has very good properties as regards thermal shock, and can be fused and sprayed without any objectionable spitting notwithstanding crosswise cracking in any quadrant.

Rods according to this invention may be made of any of the refractory oxides disclosed in the mentioned Patent 2,707,691 and rods of zirconia and rods of alumina are preferably made as described in Patents 2,876,121 and 2,882,174, with the exception that the above described slots are formed in the periphery thereof. However, this invention is not limited to the use of refractory oxides, but is also advantageous for any flame spraying rods which are subject to thermal shock. Rods other than oxides such as carbides, borides, nitrides and cermets which are subject to thermal shock and spitting during the flame spraying operation can be made to spray faster and more smoothly by using my herein described inven- .tion.

In further explanation of the advantages of the slots, the present invention teaches that it will be of a dimension that precludes an undue volume of flow back of gases and molten spray material. The dimension of the slots controls the back flow of the burning gases in a reverse direction therethrough which back flow is caused by the turbulence of the flame on the inside of the air cap 14 immediately adjacent the rod as shown in FIG. 1, which back flow tends to roll back some of the fused refractory material along the rod. With the present invention, the fused material which rolls back in the slots 11, as shown in FIG. 2, and along the surface of the rod not only helps to control the reverse flow of hot gases, but also serves to begin preheating the rod as it approaches the hottest portion of the flame. Such preheating effect contributes to the more rapid melting and spraying of the material. Preheating of the rod is useful, on the one hand, as an aid to faster spraying and yet simultaneously too great a reverse flow of hot gases is prevented. This observation substantiates the fact that the present rod provided with longitudinally extending, radially projecting slots 11 constitutes a marked improvement over rods previously provided for this purpose.

Another feature inherent in my improved slotted rod structure resides in the welding of the end of one rod onto the leading end of the next incoming rod to further control spitting. In using some flame spray rods, when the rod is about used up and the remaining tip end of the rod is presented to the oxyacetylene flame, the end is sometimes blown out of the gun nozzle with the propelling gas used for blowing the fused oxide onto the surface to be coated. The hard unfused rod end is fo-rceably projected or spit against the surface to be coated and may damage it or stick thereto as a large particle. With my fluted rod construction making use of the narrow slots I have described, some of the fused oxide material rolls backwardly along the rod and into the slots where it is cooled by the material of the rod and the fused material solidifies as the heat flows into the rod. When the leading end of a new rod follows the remaining end of a rod that has been sprayed, a slight tacking or welding of the remaining end to the leading end of an incoming rod is thus accomplished by rolling back a portion of the fused refractory material and solidifying it against the leading end of the incoming rod to hold the remaining end in place to prevent it from being spit out as has sometimes happened in the pas-t while using solid unslotted rods. The tip end of the view shown in FIG. 2 shows a remaining end 10' welded or tacked onto a leading end 10 by the rolling back of molten material that preheats the incoming rod end and then solidifies in the slots to hold the remaining end in the fusing flame to eliminate spitting.

As pointed out above, the construction provides a rod for coating articles by flame spraying utilizing self bonded particles of refractory material, as described above, and the rod will have a cross section showing a periphery formed with longitudinally extending, spaced, radially inwardly projecting, relatively narrow slots. These slots have a width between .010" and 0.30", and open into the periphery of the rod in spaced relation, the surface of the rod between the slots being substantially unobstructed. The center core indicated at 13, and defined by the bottoms of the slots, is unobstructed and has a diameter at least equal to the depth of the slots, e.g., where the rod is about inch in diameter, the center core defined by the bottoms of the slots has a diameter at least about 4; inch. While the rod is preferably generally cylindrical, it may have other shapes and preferably, as stated, the peripheral area of the rod between the slots, i.e., where they open into the periphery, is substantially unobstructed.

The following table shows a comparison of the spraying of rods of this invention with the results obtained :by spraying conventional forms of zirconia rods. In these tests, a plate of steel 6" square was placed in front of the ordinary apparatus used for performance of this type of coating process. An area approximately 4" by 4" was coated in the center of the plate in order to catch all of the fused material sprayed toward the plate which could be deposited as a coating. Each plate was weighed before and after a coating run. The length and diameter of each of the rods used was noted, along with the weight thereof. A record of the rate of rod feed per minute was kept. From this data, as recorded below, the rate of rod spraying and the efficiency of the coating lay down was computed.

Rod Feed Coating Rod Type and Width of Slots Rate Laydown Efficiency Zirconia, in inches (inches/ (lbs/hour) (percent) min.)

%-3 slots 010 4. 7 1. 19 69 %-4 slots 010 5.0 1. 26 69 015 4. 8 l. 00 61 .020 5. 6 1. 15 %6 slots 010 5. 3 1. 23 66 .015 5.5 1.18 65 %8 slots .015 6. 4 1. 30 66 020 6. 7 1. 44 69 Solid Rod (no slots) Zirconia:

2. 7 7O 66 M 3. 4 .90 65 Tubular rod (.025 hole) Zirconia:

These data show in general that the larger the number of slots, the more rapidly the material can be fused and sprayed. It is also apparent that the wider the slot, the faster the material can be sprayed. While the actual efficiency of laydown does not seem to show any general pattern as determined by the weight of the material deposited on the basis of total material sprayed, the over-all efficiency of the process, taking into account labor involved, is greatly improved as the rate of spraying is increased. A noticeable increase in the spray rate with approximately the same percent of laydown of coating material results in a substantial reduction in the ultimate cost of the coating whereby a considerable saving is shown in the above data.

While the slots provided in the periphery of the preferred form of the rods are formed as shown in the drawings and extend longitudinally along the length thereof, as has been suggested above, the slots might be spirally or otherwise arranged along the length of the rod. Also the slots may be provided with interruptions at spaced points lengthwise or slots with a tapering cross-sectional configuration may be provided. Many other modifications may occur to those skilled in the art which will fall within the scope of the following claims.

I claim:

1. For coating articles by flame spraying a rod consisting essentially of a fusible refractory material selected from the group consisitng of borides, carbides, nitrides, oxides and cermets, melting at a temperature above about 1000 C., with longitudinally extending, spaced radially inwardly projecting slots, all portions of each of the slots having a width of an order that is greater than .010" and less than .030".

2. A rod according to claim 1 wherein said rod is formed of a metal oxide.

3. A rod according to claim 2 wherein said rod is formed of alumina.

4. A rod as described in claim 3 for coating articles by flame spraying wherein the rod is about A inch in outside diameter.

5. A rod according to claim 2 wherein said rod is formed of zirconia.

6. A rod as described in claim 1 for coating articles by flame spraying wherein the center core defined by the bottoms of the slots is unobstructed and has a diameter at least equal to of an inch.

7. A rod as described in claim 1 for coating articles by flame spraying which is generally cylindrical and the peripheral area of the rod between said slots is substantially unobstructed.

References Cited UNITED STATES PATENTS 3/1959 Ault 10657 4/1959 Ault 106-67 

1. FOR COATING ARTICLES BY FLAME SPRAYING A ROD CONSISTING ESSENTIALLY OF A FUSIBLE REFRACTORY MATERIAL SELECTED FROM THE GROUP CONSISTING OF BORIDES, CARBIDES, NITRIDES, OXIDES AND CERMETS, MELTING AT A TEMPERATURE ABOVE ABOUT 1000*C., WITH LONGITUDINALLY EXTENDING, SPACED RADIALLY INWARDLY PROJECTING SLOTS, ALL PORTIONS OF EACH OF THE SLOTS HAVING A WIDTH OF AN ORDER THAT IS GREATER THAN .010" AND LESS THAN .030".
 6. A ROD AS DESCRIBED IN CLAIM 1 FOR COATING ARTICLES BY FLAME SPRAYING WHEREIN THE CENTER CORE DEFINED BY THE BOTTOMS OF THE SLOTS IS UNOBSTRUCTED AND HAS A DIAMETER AT LEAST EQUAL TO 1/10 OF AN INCH. 